A set of golf clubs usually includes three or four "woods", eight or so "irons", a putter, and perhaps some specialty clubs such as pitching and sand wedges. One of the woods, termed the driver, is used to drive the ball from the tee, while the other woods and the irons are used to hit balls on the fairway. Of course, there are instances when one would use one of the other woods or one of the irons to drive the ball from the tee.
Each club has a shaft and a head at one end. The lengths of the clubs vary as do the inclinations of the striking surfaces of the heads. The clubs which are used to drive the ball great distances have long shafts and steep striking surfaces.
Golf clubs, and in particular clubs with which this invention is primarily concerned, namely the irons, are usually manufactured in a set and bear numbers from 2 to 9. Such sets may also include a number 1 iron and other specialty irons such as the pitching and sand wedges. The loft on the face of the irons increases from the number 2 iron progressively through to the number 9 iron. Also, the length of the club decreases from the number 2 iron progressively to the number 9 iron. The combination of inclination of the surface that strikes the ball and the length of the clubs, causes the ball to travel progressively farther from the number 9 iron to the number 2 iron, while the loft or vertical height of the ball increases progressively from the number 2 iron to the number 9 iron.
It is known that the effective weight of each iron should be the same, effective in the sense that each iron feels as if it has the same weight. This is accomplished by maintaining the moment for each iron constant; that is to say, the length of the shaft times the weight of the head is the same for all irons. Also, the weight of the shaft itself is taken into consideration. Actually, it has been determined empirically that the point to measure this moment is not at the free end of the iron, but rather at a point 12 to 14 inches from the free end. All of the irons in a set are swing weighted so that when balanced at a selected point, say 12 inches from the end, the same weight can be applied to the free end of the club to balance it. The woods may be swing weighted also.
There have been efforts made from time to time to reduce the differences in feel and performance of the clubs. For example, U.S. Pat. No. 1,917,774 which issued to Ogg et al. advances the concept of maintaining constant the location of the "sweet spot". The weight of each head is redistributed such that the moments about a line passing through the center of the hitting surface of the head and the club handle are constant. Similarly, U.S. Pat. No. 1,642,462 to Reach advocates maintaining constant the location of the sweet spot.
In U.S. Pat. No. 3,059,926 to Johnstone the weight is distributed so that the optimum point of contact on the head is near the shaft for the 9 iron and is farthest from the shaft for the 1 iron, for the stated purpose of automatically imparting desired rotation to the golf ball.
There have been suggestions in the art of redistributing the weight in the head to achieve some specified object, such as U.S. Pat. No. 2,846,228 to Reach and others of the patents mentioned above.
The art has failed to take into consideration the change in feel between the clubs occasioned by the rotation of the club about its axis during the swing. Because of the golfer's anatomy, the club inherently rotates about the axis of the shaft as it is being swung. U.S. Pat. No. 3,595,577 to Hodge recognizes the existence of this twisting of the club during the swing.
It has not been heretofore recognized that each iron in a so-called matched set has a different twisting or moment about the shaft axis as it is being swung. Thus, although currently available irons are balanced in one sense to maintain the "feel" constant, the different twisting effect of each iron causes a different quantity of spin to be imparted to the ball, whereby one iron will cause the ball to hook (or slice) to one extent and another club to cause it to hook (or slice) to a different extent, making control that much more difficult. At best, a highly skilled golfer will subconsciously adjust his swing to compensate for the differences in moment about the shaft axis.